New Images Not Showing in Posts

I am suddenly having a problem adding new images to either new or old posts. I wanted to add a “signature” image at the bottom of each of my posts, but it won’t show up. I can see it when I am editing the post, but I can’t see it in the preview or if I publish the post. I’m using a linked image. I’ve tried linking different images and I’ve tried creating an entirely new post with any image and nothing is showing up. You can see the little missing image icon at the bottom of this post just before the phrase “You May Also Like”:

I just disabled the JetPack plugin’s Photon option and the image is showing up on my site now. Apparently, the Photon option isn’t working properly. It was automatically installed when I updated JetPack. It lets you host your images on the WordPress.com site, apparently. Why isn’t it working, I wonder?